1. Field of the Invention
The present invention relates to a lens barrel and an optical apparatus including the same, the lens barrel being suitable for driving a shift moving frame holding a lens for image blur correction so as to have a component in a direction orthogonal to an optical axis in order to correct an image blur due to vibration such as hand movements.
2. Description of the Related Art
In an optical apparatus such as a digital still camera and video camera, an image blur correction device has been used. Specifically, the image blur correction device detects hand movements of a user, and corrects a blur of a taken image (image blur).
In the image blur correction device, some optical elements for image blur correction (correction lens), which constitute an imaging lens, are driven in a pitch direction (longitudinal direction) and in a yaw direction (lateral direction).
With this configuration, a shift of a position of image formation due to hand movements is corrected. Thus, the image blur is cancelled (corrected).
In such image blur correction device, image blur correction may not be efficiently performed when a correction lens and a movable member (shift moving frame) movably supporting the correction lens rotate in a plane orthogonal to the optical axis.
Generally, a center of gravity of the movable member is situated at a position shifted from an axis in a direction of a thrust force generated from a driving portion for moving the movable member. Therefore, upon image blur correction, due to the thrust force, there is generated a rotational moment for rotating the movable member in the plane orthogonal to the optical axis. In addition, there is generated a force for rotating the movable member also due to vibration and friction other than the thrust force.
When the movable member is rotated in the plane orthogonal to the optical axis, the movable member may come in contact with a fixed member during image blur correction operation. As a result, driving properties of the movable member are changed, and hence the image is adversely affected.
Further, a position detection sensor for detecting a position of the movable member of the image blur correction device includes an optical sensor in many cases. The optical sensor includes a combination of a Hall element, a light emitting element, and a light receiving element, the Hall element including a combination of a magnet and a magnetic detection element. The position detection sensor is adapted for a movement of the correction lens in one of a yaw direction and a pitch direction in the plane perpendicular to the optical axis.
Here, the yaw direction is defined as a horizontal direction in the plane perpendicular to the optical axis in a posture of the camera in use. Meanwhile, the pitch direction is defined as a perpendicular direction in the plane perpendicular to the optical axis in a posture of the camera in use.
Thus, when the correction lens is rotated largely in the plane orthogonal to the optical axis, output properties of the position detection sensor are changed. As a result, it is impossible to correctly detect the position of the correction lens, and a so-called cross talk is generated. In addition, when a position detection property is changed due to rotation of the correction lens, feedback position control causes anomalous oscillation. Further, optical performance upon correction of hand movements is deteriorated.
In rotation of the correction lens within such an amount that the feedback position control is allowed, feedback position control can be performed in order to position the correction lens to a target position. However, the above-mentioned feedback position control leads an increased electric power consumption.
Conventionally, there has been known an image blur correction device. Specifically, in the image blur correction device, a correction lens held by a movable member is displaced in any one of a yaw direction and a pitch direction without being rotated about an optical axis (Japanese Patent Application Laid-Open No. H05-297443 and Japanese Patent Application Laid-Open No. H10-319465).
Japanese Patent Application Laid-Open No. H05-297443 discloses an image blur correction device provided with a guide shaft for regulating rotation. In addition, Japanese Patent Application Laid-Open No. H10-319465 discloses an image blur correction device in which rotation is prevented with a tension coil spring.
In the image blur correction device in Japanese Patent Application Laid-Open No. H05-297443, a gimbal structure is employed. With this structure, the correct lens is held by two guide shafts so as to be guided by the two guide shafts. Thus, the correct lens is allowed to move in any one of a yaw direction and a pitch direction, which are defined as two axial directions orthogonal to each other in the same plane. For image blur correction, response within a frequency band of several 10 Hz is needed, and also for position accuracy, high accuracy control is required. Therefore, it is essential to hold the correct lens with little friction and little backlash.
Therefore, In Japanese Patent Application Laid-Open No. H05-297443, in order to accurately displace the correction lens in the same plane, it is preferred that the two guide shafts be fitted into each other at two points. However, in order to hold those two guide shafts, which are fitted into each other at two points, without backlash but with high accuracy, a more complex structure is required.
In addition, in this structure, a rotational moment for rotating the movable member remains, and a torsion force is generated between the guide shafts and a bearing provided to the moving frame when the movable member is displaced. Therefore, it is difficult to satisfactorily maintain micro-amplitude properties.
In a lens shifting device of Japanese Patent Application Laid-Open No. H10-319465, a movable member holding a correction lens is supported in parallel to a plane perpendicular to the optical axis with at least three balls rotatably held by a fixed member. Further, by an elastic member provided for generating a pressing force for sandwiching the three balls between the movable member and the fixed member, rotation of the movable member about the optical axis is prevented.
In this case, rolling friction of the three balls is lower than sliding friction acting between a guide shaft and a bearing. Therefore, it is possible to satisfactorily maintain the micro-amplitude properties of the correction lens due to a friction of a mechanical mechanism.
In this case, when a center of the correction lens most frequently used is situated in vicinity of the optical axis, if, in a driving direction of the movable member, a force from the elastic member is not applied uniformly to the movable member from both sides, the force from the elastic member acts as a load. As a result, the electric power consumption increases. In addition, a unit for uniformly applying, in the driving direction of the movable member, the force from the elastic member to the movable member is required.
Meanwhile, in recent years, an image pickup element (charge coupled device (CCD) and complementary metal oxide semiconductor (CMOS)) for converting a subject image, which is formed by means of an photographic optical system, into an electrical signal has a shorter pixel pitch by grace of development of a semiconductor micro-processing technology. Moving amount of a shift lens group for correcting hand movements having the same amount is substantially proportional to an image pickup area. For this reason, when the pixel pitch of the image pickup element is shorter, it is more difficult to satisfactorily correct the image blur without more micro movement having a higher accuracy.